Shamanism refers to a range of traditional beliefs and practices concerned with communication with the spirit world. There are many variations of shamanism throughout the world, though there are some beliefs that are shared by all forms of shamanism:

The spirits can play important roles in human lives. The shaman can control and/or cooperate with the spirits for the community's benefit. The spirits can be either good or bad. Shamans engage various processes and techniques to incite trance; such as: singing, dancing, taking entheogens, meditating and drumming. Animals play an important role, acting as omens and message-bearers, as well as representations of animal spirit guides. The shaman's spirit leaves the body and enters into the supernatural world during certain tasks. The shamans can treat illnesses or sickness. Shamans are healers, gurus and magicians. Shamans have the ability to diagnose and cure human suffering and, in some societies, the ability to cause suffering. This is believed to be accomplished by traversing the axis mundi and forming a special relationship with, or gaining control over, spirits. Shamans have been credited with the ability to control the weather, divination, the interpretation of dreams, astral projection, and traveling to upper and lower worlds. Shamanistic traditions have existed throughout the world since prehistoric times.

Some anthropologists and religious scholars define a shaman as an intermediary between the natural and spiritual world, who travels between worlds in a state of trance. Once in the spirit world, the shaman would commune with the spirits for assistance in healing, hunting or weather management. Ripinsky-Naxon describes shamans as, “People who have a strong interest in their surrounding environment and the society of which they are a part.”

Other anthropologists critique the term "shamanism", arguing that it is a culturally specific word and institution and that by expanding it to fit any healer from any traditional society it produces a false unity between these cultures and creates a false idea of an initial human religion predating all others. However, some others say that these anthropologists simply fail to recognize the commonalities between otherwise diverse traditional societies.

Shamanism is based on the premise that the visible world is pervaded by invisible forces or spirits that affect the lives of the living. In contrast to animism and animatism, which any and usually all members of a society practice, shamanism requires specialized knowledge or abilities. It could be said that shamans are the experts employed by animists and animist communities. Shamans are often organized into full-time ritual or spiritual associations, like priests.Source:http://en.wikipedia.org/wiki/Shamanism